Cationic UV-crosslinkable acrylic polymers for pressure sensitive adhesives

ABSTRACT

An ultraviolet (UV) crosslinkable acrylic pressure sensitive adhesive comprises an acrylic copolymer and a cationic photoinitiator. The acrylic copolymer comprises pendant reactive functional groups. The pressure sensitive adhesive formed from the acrylic copolymer with the pendant reactive functional groups result in high green strength and/or high temperature holding strength of the adhesive.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/US2011/27632 filed Mar. 9, 2011, which claims the benefit ofU.S. Provisional Patent Application No. 61/311,970 filed Mar. 9, 2010,the contents of both of which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to an ultra-violet curable pressure sensitiveadhesive comprising an acrylic polymer with pendant reactive functionalgroups.

BACKGROUND OF THE INVENTION

Pressure sensitive adhesives (PSAs) are aggressive and permanently tackyat room temperature and adhere to surfaces by application of lightfinger pressure. PSA compositions are commonly applied to varioussubstrates, such as paper, fabric, metal, and plastic films that arethen converted into a large number of different products, especiallypressure sensitive adhesive tapes and labels. These pressure sensitiveadhesive products have a broad field of application in the automobileindustry, e.g., for fastening or sealing, in the pharmaceuticalindustry, e.g., for bandages or transdermal drug delivery systems, or inthe packaging industry, e.g., for sealing, bonding or labeling.

PSAs can be formulated for application as a solvent borne or a moltenadhesive. Hot melt pressure sensitive adhesives (HMPSAs) arecompositions that combine the properties of hot melt adhesives withthose of pressure sensitive adhesives. Hot melt adhesives are solids atroom temperature, melt at elevated temperatures to coat on a substrate,and regain their solid form on cooling. The combination of theseproperties provides compositions that melt at elevated temperatures andcool to form a permanently tacky solid coating that adheres on contact.A good workable HMPSA must exhibit high cohesive strength at roomtemperature, low shrinkage on substrates, retention of pressuresensitive properties during storage and use, and a relatively fluidviscosity at typical coating temperatures (e.g., between 80° C. and 180°C.). Although very low molecular weight polymers will yield hot meltadhesives with sufficient fluidity, the resulting adhesives lackcohesive strength. Very high molecular weight polymers give bettercohesive strength, but are too viscous at the common applicationtemperatures to be easily coatable on substrates. They must be blendedwith a high proportion of low molecular weight oils or resins to reducethe viscosity. The addition of low molecular weight oils or resins inturn detracts from the cohesive strength and heat resistance. To avoidthese problems, polymers of moderate molecular weight have been madewith various functional groups which undergo crosslinking reactions byheat or actinic radiation. In this manner, the cohesion of acrylic PSAscan be raised by means of sufficient crosslinking.

Acrylic polymers with epoxy functional groups have been known in priorart. An example of such polymers are described in JP1186876, however,these polymers fail to crosslink under UV radiation and/or heat.

JP2008-208149 is directed to acrylic copolymers with non free radicalpolymerizable oxetane compounds as a polymerization medium and reactivediluent. The polymerization is completed with heat and/or x-rayirradiation to form an adhesive for a flat panel display.

JP 08-060127 and 199606127 describe UV-curable acrylic polymers butrequire the addition of multifunctional polyol and otherhydroxyl-functional groups for crosslinking the polymers.

JP2003147311 is directed to the use of photopolymerizable diacrylate.Due to the difunctional acrylate which crosslinks upon radicalpolymerization, it is less desirable for use in an adhesive, andespecially unsuitable for a solvent borne or hot melt adhesive, becauseit is necessary to polymerize the acrylate monomers followingapplication onto the final coated substrate.

There is an ongoing demand and a continuing need in the art forUV-crosslinkable acrylic polymers that can be formulated as solventborne adhesives and/or that are hot melt processable. The currentinvention addresses this need by providing acrylic polymers that arefunctionalized with pendant reactive functional groups and cationicphotoinitiators and, following the coating operation, are crosslinkedunder UV irradiation on the substrates. The invention provides the artwith both solvent borne acrylic PSAs and hot melt acrylic PSAs.

SUMMARY OF THE INVENTION

The invention provides cationic ultra-violet-curable pressure sensitiveadhesive comprising (a) crosslinkable acrylic polymers which comprisependant reactive functional groups and (b) a cationic photoinitiator.

In one embodiment, the crosslinkable acrylic polymer (a) of the adhesivecomprises (i) an acrylic monomer which is an acrylic or methacrylic acidderivative of the formula CH₂═CH(R₁)(COOR₂), wherein R₁ is H or CH₃ andR₂ is C₁₋₂₀ alkyl chain and (ii) a monomer with a pendant reactivefunctional group selected from cycloaliphatic epoxide, oxetane ormixtures thereof, and the amount of the monomer (ii) is from about 0.001to about 0.015 equivalent per 100 g of the acrylic polymer. The acrylicpolymer is essentially free of multi-(meth)acrylate, polyol orOH-functional groups and the polymer remains substantially linear afterpolymerization.

In another embodiment, the crosslinkable acrylic polymer (a) of theadhesive comprises (i) an acrylic monomer which is an acrylic ormethacrylic acid derivative of the formula CH₂═CH(R₁)(COOR₂), wherein R₁is H or CH₃ and R₂ is C₁₋₂₀ alkyl chain and (ii) a monomer with acombination of pendant reactive functional groups selected from (1)cycloaliphatic epoxide, oxetane, benzophenone or mixtures thereof, and(2) mono-substituted oxirane; and the amount of the monomer (ii) is theamount of about 0.001 to about 0.015 equivalent per 100 g of the acrylicpolymer. The acrylic polymer is essentially free ofmulti-(meth)acrylate, polyol or OH-functional groups and the polymerremains substantially linear after polymerization.

In a further embodiment, the cationic photoinitiator (b) the adhesivehas the structure of

where R is C₃H₇, C₁₂H₂₅, W is S, SO, SO₂ or CO.

In another embodiment, the cationic ultra-violet-curable pressuresensitive adhesive further comprises a polyethylene copolymer additive,plasticizer, fillers, inhibitors, antioxidants, accelerators, tackifierand/or solvent.

A further embodiment is directed to a method of preparing acrosslinkable acrylic polymer which comprises pendant reactivefunctional groups.

Yet another embodiment is directed to an article manufactured using theadhesives of the invention. The adhesive is in a form of a solvent borneacrylic pressure sensitive adhesive or an acrylic hot melt pressuresensitive adhesive. The adhesive article further comprises a backingwhich is a polyester, polypropylene, metal or glass. The adhesives areparticularly advantageous as a tape, an adhesive transfer film, adecorative or protective film, decal or label.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a graph of viscosity over time at 130° C., measured byBrookfield viscometer.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides the art with acrylic polymers comprisingUV-reactive pendant functional groups bound to the polymer chain.Depending upon the bound functional groups, the acrylic polymerundergoes fast UV-crosslinking reaction and provides green strengthand/or undergoes post-UV crosslinking in the presence of a cationicphotoinitiator to results in adhesives with high cohesive strength andhigh temperature holding strength.

The choice and relative amount of the specific acrylic and vinylmonomers making up the acrylic polymers used in preparing the adhesivesof this invention depend upon the desired final properties andcontemplated end uses of the adhesives. The choices of which acrylic andvinyl monomers and their relative amounts in the final composition toachieve the desired properties are within the expertise of those skilledin the art.

In one embodiment of the invention, the acrylic polymers are thosehaving the following composition or those that can be prepared bypolymerizing (i) an acrylic monomer which is an acrylic or methacrylicacid derivative (e.g. methacrylic acid ester) of the formulaCH₂═CH(R¹)(COOR²), where R¹ is H or CH₃ and R² is a C₁₋₂₀, preferablyC₁₋₈, alkyl chain and (ii) a monomer with a pendant reactive functionalgroup, which is described in more detail herein below, and the amount ofthe monomer (ii) is from about 0.001 to about 0.015 equivalent per 100 gof the acrylic polymer. In a more preferred embodiment, the amount ofthe monomer is from about 0.002 to about 0.01 equivalent per 100 g ofthe acrylic polymer.

For the polymerization process of the invention the monomers ofcomponents (i) and (ii), where appropriate, are converted by radicalpolymerization into acrylic polymers. In polymerization, the monomersare chosen such that the resulting polymers can be used to prepareadhesives, especially such that the resulting polymers possess pressuresensitive adhesive properties in accordance with the “Handbook ofPressure Sensitive Adhesive Technology” by Donatas Satas (van Nostrand,N.Y. 1989).

Examples of acrylates and/or methacrylates useful as components ofmonomer mixture (i) include methyl acrylate, ethyl acrylate, ethylmethacrylate, methyl methacrylate, n-butyl acrylate, n-butylmethacrylate, n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate,and n-octyl acrylate, n-nonyl acrylate, lauryl methacrylate, cyclohexylacrylate, and branched (meth)acrylic isomers, such as i-butyl acrylate,i-butyl methacrylate, n-butyl methacrylate, 2-ethylhexyl acrylate,stearyl methacrylate, and isooctyl acrylate. The exemplary acrylatesand/or methacrylates are mono-acrylic monomers, and do not include anydi or multi-acrylate monomers.

The exemplary acrylic monomer mixture (i) has a Tg value less than 0° C.and a weight average molecular weight from about 10,000 to about2,000,000 g/mol more preferably between 50,000 and 1,000,000 g/mol andmost preferably between 100,000 and 700,000 g/mol. The mixture (i) maybe a single monomer provided that its homopolymer Tg is less than 0° C.

Suitable monomer (ii) of the polymer is capable of undergoing cationicUV-activated crosslinking reaction and providing green strength to theadhesive films, include cycloaliphatic epoxide monomers M100 and A400(Daicel), oxetane monomer OXE-10 (Kowa Company), dicyclopentadienylmethacrylate (CD535, Sartomer Co., PA) epoxide,4-vinyl-1-cyclohexene-1,2-epoxide (Dow). Other exemplary monomers (ii)include vinyl or acrylic compounds containing cationic UV-reactivefunctional groups with the formula (1):

whereR¹ is O, S, C═O, or linear, branched, or cyclic alkylene, oxyalkylene,or arylene,R² is linear, branched, or cyclic alkyl, or alkoxy, aryl, H, halogen,C═O, or part of R¹ as fused cycloaliphatic ring through a covalent bondconnection,R³ is (CH₂)_(n), n=0-3,X is acrylate, methacrylate or comprises a —W—Y group, whereW is O, S, amide, carbonate, urethane, urea, siloxane or a combinationthereof, andY is —R⁴—C(R⁵)═CH₂, where R⁴ is a linear or branched C₂₋₁₀ alkylene orC₂₋₁₀ oxyalkylene, arylene, or derivatives thereof, and R⁵ is H or CH₃.

A preferred vinyl or acrylic compound for use as monomer (ii) isrepresented by the structural formula (1A):

where R²═H or CH₃,

Another preferred vinyl or acrylic compound for use as monomer (ii) isrepresented by the structural formula (1B):

Another preferred vinyl or acrylic compound for use as monomer (ii) isrepresented by the structural formula (1C):

Yet another preferred vinyl or acrylic compound for use as monomer (ii)is represented by the structural formula (1D):

Yet another preferred vinyl or acrylic compound for use as monomer (ii)is represented by the structural formula (1E):

Yet another preferred vinyl or acrylic compound for use as monomer (ii)is represented by the structural formula (1F):

Yet another preferred vinyl or acrylic compound for use as monomer (ii)is represented by the structural formula (1G):

where R⁶═H or CH₃.

Yet another preferred vinyl or acrylic compound for use as monomer (ii)is represented by the structural formula (1H):

where R═H or C₁₋₁₃.

In another embodiment of the invention, the acrylic polymers are capableof undergoing post-UV cationic activated reaction and thus, provide hightemperature holding strength to the adhesive films. The acrylic polymersare those having the following composition or those that can be preparedby polymerizing (i) an acrylic monomer which is an acrylic ormethacrylic acid derivative of the formula CH₂═CH(R₁)(COOR₂), wherein R₁is H or CH₃ and R₂ is C₁₋₂₀ alkyl chain and (ii) a monomer with acombination of pendant reactive functional groups selected from both (1)cycloaliphatic epoxide, oxetane, benzophenone or mixtures thereof, and(2) mono-substituted oxirane. The amount of the monomer (ii) is theamount of about 0.001 to about 0.015 equivalent per 100 g of the acrylicpolymer. The acrylic polymer is essentially free ofmulti-(meth)acrylate, polyol or OH-functional groups and the polymerremains substantially linear after polymerization. In a more preferredembodiment, the amount of the monomer (ii) is from about 0.002 to about0.01 equivalent per 100 g of the acrylic polymer.

Examples of suitable acrylic monomer mixture (i) have been describedherein.

Examples of monomer (ii) with cycloaliphatic epoxide and oxetane pendantreactive functional groups (1) have also been described herein.

Suitable monomer (ii) with benzophenone pendant reactive function groups(1) include the compounds of the following formula (2), (3), and (4):

whereZ is S, O, CH₂, or NH,R¹⁻⁸ are independently H, Cl, Br, I, F, C₁₋₂₄ alkoxy, C₁₋₂₄ alkyl, oraryl; and wherein at least one of R¹⁻⁸ must comprise a —W—X—Y group,whereW is a C₁₋₁₂ alkylene or C₁₋₁₂ oxyalkylene,X is carbonate, urethane, urea, tetramethyldisiloxane or a combinationthereof, andY is —R⁹—C(R¹⁰)═CH₂, where R⁹ is a linear or branched C₂₋₁₀ alkylene orC₂₋₁₀ oxyalkylene, arylene, or derivative thereof, and R¹⁰ is H or CH₃.

A preferred vinyl or acrylic compound for use as monomer (ii) isrepresented by the structural formula (3A):

where n=1-12, preferably n=1.

Another preferred vinyl or acrylic compound for use as monomer (ii) isrepresented by the structural formula (3B):

where n=1-12, preferably n=1.

Yet another preferred vinyl or acrylic compound for use as monomer (ii)is represented by the structural formula (3C):

Yet another preferred vinyl or acrylic compound for use as monomer (ii)is represented by the structural formula (3D):

Another preferred vinyl or acrylic compound for use as monomer (ii) isrepresented by the structural formula (4A):

where n=1-12, preferably n=1.

Exemplary mono-substituted oxirane (2) of monomer (ii) include glycidylmethacrylate (GMA), 1,2-epoxy-5-hexene, 4-hydroxybutylacrylate glycidylether (4-HBAGE), cycloaliphatic epoxide monomer M100 and A400, OXE-10,CD535 epoxide, 4-vinyl-1-cyclohexene-1,2-epoxide. Another example ofsuitable reactive functional group has the following formula (5A):

The invention also provides the art with UV-crosslinkable adhesivescomprising the acrylic polymers herein and a cationic photoinitiator.

The primary function of a photoinitiator is to initiate crosslinkingreaction when the photoinitiator is irradiated with UV radiation. Thereare two main types of photoinitiators that can be used in this inventionto initiate the crosslinking upon irradiation: radical photoinitiatorsand cationic photoinitiators.

The most frequently used cationic photoinitiators are either organiciodonium or sulfonium salts. The mechanism of a cationic photoinitiator,when irradiated, is that it forms an excited state which then breaksdown to release a radical cation. This radical cation reacts with thesolvent, or other hydrogen atom donors, and generates a protonic acid,which is the active species that initiates the crosslinking reaction.

Any of the many compounds known to initiate polymerization by a cationicmechanism may be used for the crosslinking reaction in this invention.These include, for example, diaryliodonium salts, triarylsulfoniumsalts, dialkylphenylsulfonium salts,dialkyl(hydroxydialkylphenyl)sulfonium salts and ferrocenium salts. Theanions in theses salts generally possess low nucleophilic character andinclude SbF₆ ⁻, PF₆ ⁻, AsF₆ ⁻, BF₄ ⁻, B(C₆F₅)₄ ⁻ or Ga(C₆F₅)₄ ⁻.Specific examples include Cyracure UVI-6976 (Dow Chemical). Particularlyuseful cationic initiators are soluble and red-shifted sulfonium saltphotoinitiators, which have increased solubility in UV-crosslinkablecompositions, promote efficient thick film UV curing, and exhibitincreased thermal stability in UV crosslinkable compositions beforecure, exhibit increased curing rates, and have a reduced dark cure time,having the structural formula (6A) and (7A):

where R is C₃H₇, C₁₂H₂₅, W is S, SO, SO₂ or CO.

where R¹ and R² are independently H, CH₃, C₂H₅, C₃H₇, C₁₂H₂₅, OCH₃,OC₂H₅, OC₃H₇, or OC₁₂H₂₅.

The adhesive may also comprise various other additives, such asplasticizers, tackifiers, and fillers, all of which are conventionallyused in the preparation of PSAs. As tackifier or tackifying resins to beadded, it is possible to use any known tackifying resins described inthe literature. Non-limiting examples include pinene resins, indeneresins, and their disproportionated, hydrogenated, polymerized, andesterified derivatives and salts, the aliphatic and aromatic hydrocarbonresins, terpene resins, terpene-phenolic resins, C₅ resins, C₉ resins,and other hydrocarbon resins. Any desired combinations of these or otherresins may be used in order to adjust the properties of the resultantadhesive in accordance with the desired final properties.

In general, it is possible to use any resin which is compatible with thecorresponding acrylic polymers; reference may be made in particular toall aliphatic, aromatic, alkylaromatic hydrocarbon resins, hydrocarbonresins based on hydrocarbon resins, hydrogenated hydrocarbon resins,functional hydrocarbon resins, and natural resins. Explicit referencemay be made to the depiction of the state of the art in the “Handbook ofPressure Sensitive Adhesive Technology” by Donatas Satas (van Nostrand,1989).

In a further advantageous development, one or more plasticizers, such aslow molecular weight acrylic polymers, phthalates, benzoates, adipates,or plasticizer resins, are added to the acrylic HMPSAs.

The acrylic PSAs may further be blended with one or more additives suchas aging inhibitors, antioxidants, light stabilizers, compoundingagents, and/or accelerators.

The adhesive may further be mixed with one or more fillers such asfibers, carbon black, zinc oxide, titanium dioxide, solid or hollowglass microbeads, microbeads of other materials, silica, silicates, andchalk.

For the inventive process it may further be of advantage to addcompounds to the acrylic PSAs that facilitate subsequent crosslinking.For this purpose the copolymers may optionally be blended withcrosslinkers. Examples of suitable crosslinkers are functionalacrylates. Preferred substances in accordance with the inventive processin which crosslinking occurs under radiation are, for example,difunctional or trifunctional acrylates, difunctional or polyfunctionalurethane acrylates, difunctional or trifunctional or multi-functionalacrylic epoxy resins such as Lumicryl 1000 and 1100 (Estron Chemical).It is, however, also possible here to use any further difunctional orpolyfunctional compounds which are familiar to the skilled worker andare capable of crosslinking acrylic polymers. For optional thermal ormoisture crosslinking it is possible to use blocked difunctional orpolyfunctional isocyanates, (meth)acrylates or other functional groups.

One further development that makes the process of the inventionparticularly advantageous for the production of hot melt PSAs is thatall additives are either blended to the molten, solvent-free acrylicpolymers, or more efficiently, added into the solutions of thecopolymers at the end of the polymerization reactions. Upon the removalof the solvent, the mixtures are concentrated to give hot melt PSAs.

As known by those skilled in the art, the preparation of acrylicpolymers can be carried out by solution, emulsion, or bulkpolymerization procedures using well-known polymerization techniques,such as free radical techniques. The copolymers can then be formed intohot melt adhesives by removal of the solvent, coagulation of the latex,or melt-processing of the neat polymers.

The polymerization may be conducted in the presence of one or moreorganic solvents and/or in the presence of water. Suitable organicsolvents or mixtures of solvents are alkanes, such as hexane, heptane,octane, isooctane, and cyclohexane; aromatic hydrocarbons, such asbenzene, toluene, and xylene; esters, such as ethyl, propyl, butyl andheptyl acetate; halogenated hydrocarbons, such as chlorobenzene;alkanols, such as methanol, ethanol, iso-propanol, ethylene glycol, andethylene glycol monomethyl ether; ethers, such as diethyl ether anddibutyl ether; or mixtures thereof.

In one advantageous embodiment of the process, the polymerizationreactions proceed in an ethyl acetate solvent, thermally initiated by,for example, azobisisobutyronitrile (AIBN).

The acrylic polymers prepared will generally have a weight averagedaverage molecular weight (M_(w)) of from 10,000 to 2,000,000 g/mol, morepreferably between 50,000 and 1,000,000 g/mol and most preferablybetween 100,000 and 700,000 g/mol. The M_(w) is determined by gelpermeation chromatography (GPC) or matrix-assisted laserdesorption/ionization mass spectrometry (MALDI-MS).

The acrylic polymers can be prepared by polymerizing monomer mixtures of(i) and (ii). Alternatively, preparation of the UV-crosslinkable acrylicpolymers may comprise a two step reaction: (1) preparing acrylicpolymers that have pendant isocyanate functionality by using m-TMI®(3-isopropenyl-α,α-dimethylbenzyl isocyanate, Cytec) or MOI(2-methacryloyloxyethyl isocyanate, Showa Denko) as a co-monomer inpolymerization reactions; and then (2) reacting the pendant isocyanategroups with hydroxyl-functionalized epoxide, oxetane, or benzophenone.

The acrylic polymer does not contain any multi-functional acrylate andis substantially linear in its structure before UV crosslinkingreaction. Therefore, the acrylic polymer, before crosslinking, iscompletely soluble in many organic solvents, and can also be easilyapplied on substrates in solvent-free form as a hot melt adhesive.

The adhesives can be formulated as a solvent borne adhesive and used bycoating films or paper with polymer solutions or suspensions andsubsequently removing the solvent by drying.

To be used as hot melt PSAs, the acrylic polymers must be free of thesolvent. For this purpose the copolymers prepared as described above areconcentrated to a solvent content of less than 2% by weight, preferablyless than 0.2% by weight. This process takes place preferably in areaction tank, or vacuum mixer, concentration extruder, such as ventextruder, ring extruder, single-screw extruder, or twin-screw extruder,which are known to the skilled worker.

Application of the hot melt PSAs may be accomplished using anyconventional means, such as roller, slot orifice, spray, or extrusioncoating. Non-limiting examples of substrate are films, tapes, sheets,panels, foam, and the like; and can be made of materials such as paper,fabric, plastic (polyesters, PE, PP, BOPP, and PVC), nonwoven fiber,metal, foil, glass, natural rubber, synthetic rubber, wood, or plywood.If a coated substrate is to be used in the form of a self-wound roll,the back of the substrate is usually coated with a release coating toprevent the adhesive from adhering to the reverse side of the substrate.If a substrate is to be coated with the adhesive on both sides androlled, a strippable paper or other protective means is laid over theadhesive on one side to prevent that adhesive from adhering to theadhesives on the other. In some uses, a second substrate may be applieddirectly to the adhesive.

In most pressure sensitive adhesive uses, a hot melt adhesive is appliedto a backing or substrate before crosslinking. The adhesive isformulated preferably to provide a composition that can be heated torender a coatable fluid on the substrate. Commonly used industrialcoating temperatures are in the range of 80-180° C. Typically, the hotmelt PSAs of this invention have melt viscosities between 1000-500,000mPa·s, preferably between 5000-100,000 mPa·s at those applicationtemperatures.

A pressure sensitive adhesive film may be formed by applying the hotmelt to a release liner, such as silicone coated paper or plastic film,and then after irradiation, the adhesive may be stripped from therelease liner and used as a film. Alternatively, the adhesive can becoated onto a release liner, laminated and transferred to a substrate.

The hot melt PSAs of the invention can be crosslinked in air byirradiation with UV light in the range from 200 to 500 nm, preferably280 to 400 nm. Irradiation may be done immediately while the adhesivecompositions are still in a melt form, or after they have been cooled toroom temperature.

Adhesive composition is irradiated for a period of time sufficient totransform the low cohesion composition into a viscoelastic adhesive ofhigher modulus. The exact length of the exposure is dependent upon thenature and intensity of the radiation, the amount of cationicphotoinitiator, the polymer composition, adhesive formulation, thethickness of the adhesive film, environmental factors, and the distancebetween the radiation source and the adhesive film. The dosage or thelength of exposure is conveniently controlled by the belt speed. It maybe appropriate to adapt the lamp output to the belt speed or to shadeoff the belt partly, in order to reduce its thermal load.

Actinic light from any source may be used on the adhesive, provided thesource furnishes an effective amount of UV radiation. Suitable sourcesof radiation are carbon arcs, mercury-vapor arcs, fluorescent lamps withspecial ultraviolet light emitting phosphors, electronic flash lamps andthe like, lasers of specific wavelengths, UV LED, or combinations ofthose. Preferred lamps are the electrodeless microwave powered lampsfrom Fusion Systems, or commercially customary high or medium pressuremercury lamps with an output of, for example, from 80 to 240 W/cm. Theadhesive compositions of the invention generally exhibit their maximumsensitivity to wavelengths in the ultraviolet range.

In addition, the acrylic hot melt PSAs described in accordance with theinvention may be crosslinked with electron beams. This type ofcrosslinking can also take place in addition to the UV crosslinking.

The adhesives of the present invention may be used to bond one substrateto a second substrate. Substrates include but are not limited toplastic, glass or plastic-coated glass, wood, metal, etc. The adhesivemay be applied by a variety of methods including coating or spraying inan amount sufficient to cause the substrates to be bonded together toadhere. The adhesive coated substrate may be irradiated before or afterbonding. Since cure begins immediately upon irradiation, but may not becompleted for several days, there is time immediately after irradiation,but before gelation for bonding to take place.

The pressure sensitive adhesives of the invention may advantageously beused in the manufacture of adhesive articles including, but not limitedto, industrial tapes and transfer films. Single and double face tapes,as well as supported and unsupported free films are encompassed by theinvention. In one embodiment, the adhesive article comprises an adhesivecoated on at least one major surface of a backing having a first andsecond major surface. Useful backing substrates include, but are notlimited to foam, metal, paper, fabric, and various polymers such aspolypropylene, polyamide, polyester, polyethylene terephthalate, andmixtures thereof. The adhesive may be present on one or both surfaces ofthe backing. When the adhesive is coated on both surfaces of thebacking, the adhesive coatings can be the same or different.

The following examples are provided for illustrative purposes only.

EXAMPLES

Adhesive samples were tested according to the following test methods forpressure sensitive tapes, some of which were developed by the PressureSensitive Tape Council (PSTC) or by FINAT (Féderation INternationale desfabricants et transformateurs d'Adhésifs et Thermocollants sur papier etautres supports).

Gel Fraction

The percent gel fraction was used as an indication of crosslinking leveland photoinitiator efficiency.

A sample of UV-irradiated acrylic polymer (or formulated adhesive) wasseparated from the silicone release liner and weighed to the nearest 0.1mg. The sample was then placed in a glass jar and immersed in toluenefor 24 to 48 hours. The ratio of the sample mass after tolueneextraction to the initial mass gave the gel fraction expressed as apercentage. If the sample was a formulated adhesive, the mass of anytoluene-soluble component such as a tackifying resin was subtracted fromthe initial weight.

Preparation of Adhesive Coatings

A lab coater with two heatable rolls was used to apply the adhesive. Theadhesive was heated to 150° C. and coated onto a 2 mil (51 μm) thicksilicone-coated PET release liner. The adhesive on the liner wasirradiated at a line speed of 15 meters per minutes under H-bulb (FusionSystems) with a dosage of UV C 257 mJ/cm². The film was then laminatedand transferred to a polyethylene terephthalate substrate (Mylar®,DuPont) and conditioned at 23° C. and 50% relative humidity. Unlessotherwise indicated, the adhesive film thickness was 3.5 mil (89 μm).

UV Cure

Adhesive films were cured using medium pressure mercury arc lamps (usingan IST UV curing laboratory unit). The UV C dose was measured andrecorded using an EIT Power Puck. UV C is the region between 200 and 280nm.

Loop Tack

Loop Tack was measured according to Test Method B, PSTC-16, adapted asfollows. A loop tack tester was used for the measurement. All testsamples of the acrylic polymers were UV-irradiated according to theprocedure described above. The adhesive was coated on 50 μm PET filmbacking and the size of a specimen strip was 125 mm×24 mm.

Peel Adhesion

Adhesives were cast in a range of coating weights (from 20-100 g/m²)film onto a silicone liner using a Chemsultants® hot melt laminatorcoater then cured (as noted above). The cured free film was transferredto 50 μm PET backing film.

Peel adhesion was measured as the force required to remove a pressuresensitive tape from a standard stainless steel panel at a specifiedangle and speed according to FINAT Test Method no. 1 adapted as follows.Equipment used to measure this value included a standard FINAT 2 kgrubber-covered roller, and a standard Instron® tensile testing machine.

A stainless steel panel (AFERA steel from Rocholl GmbH) was cleaned asper standard FINAT method. Before the stainless steel panel was used itwas abraded along the length of the test panel with a 400-gritwaterproof wet and dry sanding paper under the tap, until water flowedsmoothly over the steel plate. After this it was rinsed with water anddried, cleaned with ethyl acetate, and conditioned in a controlledclimate room maintained at 23° C. and 50% relative humidity (RH), for atleast 1 hour.

The coating to be tested was conditioned for 24 hours at 23° C.±2° C.and 50%±5% RH. Test strips were cut to 25 mm×175 mm.

The backing paper was removed from each strip and placed, adhesive sidedown, onto a clean test plate using light finger pressure, and thenrolled twice in each direction with the standard 2 kg FINAT test roller,at a speed of approximately 10 mm per second. After applying the stripsto the test plate at a rate of one per 2 minutes the strips were leftuntil the first test piece had either 20 minutes or 24 hours elapsedtime (dwell).

The tensile tester was set with a crosshead speed of 300 mm/minute. Thefree end of the tape was doubled back at an angle of 180° and clamped tothe upper jaw of the machine. The end of the panel was clamped to thelower jaw. The test strip was then peeled from the panel and the peelforce was recorded in Newtons/25 mm width of tape.

The results obtained for adhesive mode failure were classified asAdhesion Failure (test piece separated from test plate without leavingany residue) or Cohesive Failure (adhesive film split cohesively andresidue left on test piece and test plate).

Shear Adhesion Failure Temperature (SAFT)

Three samples, 25 mm×100 mm in dimensions, were cut from each curedsample in the machine coating direction. SAFT panels (mirrored Steel)were cleaned with ethyl acetate. Samples were adhered to the steel paneloverlapping up to an engraved line so that a square 25×25 mm of adhesivewas in contact with the test panel. The test area was rubbed using astraight edged wooden applicator to ensure good contact between thepanel and test sample. Samples were placed into the test oven at roomtemperature. The heating program was started and 1 kg shear load appliedwhen the temperature reached 40° C. The oven temperature was ramped at0.5° C./minute up to 200° C. and the failure temperature (SAFT) wasrecorded.

Shear Resistance

Shear Resistance from a stainless steel surface was measured accordingto FINAT Test Method no. 8 adapted as follows. Three samples, 25 mm×100mm in dimensions, were cut from each cured coating in the machinedirection. Shear panels (pregritted steel) were cleaned with ethylacetate. Samples were adhered to the steel panel up to the engraved lineso that a square 25×25 mm of adhesive was in contact with the testpanel. The test area was rubbed using a straight edged wooden applicatorto ensure good contact between the panel and test sample. The testspecimens were conditioned for 15 minutes at 23° C.±2° C. and 50%±5% RH.They were then mounted in the test fixture and a 1 or 2 kg weightapplied. The time to failure was recorded.

Hot Shear Resistance

The above procedure for shear resistance was followed except that thetest specimens were placed into a preheated oven at 70° C., and left toacclimatize for 10 minutes. A 1 kg weight was applied and the time tofailure recorded.

Viscosity

Viscosity was measured by Brookfield DV-I Viscometer at 135° C., asshown in FIG. 1. A 10 g sample was used with a spindle No 27 at a speedsetting of 4 rpm.

Example 1

A 500 mL three-necked round bottom flask was equipped with a refluxcondenser, addition funnel and magnetic stirrer, and placed under gentlenitrogen flow. The flask was charged with 1,1,3,3-tetramethyldisiloxane(TMDS, 364 mL, 2.06 mol). The addition funnel was charged with allylalcohol (20.0 g, 0.34 mol). Approximately 2 mL of allyl alcohol wasadded to the reaction flask. The heating bath temperature was raised to50° C., at which point chlorotris(triphenylphosphine) rhodium (40 ppm or18.7 mg) was added to the reaction flask. The internal reactiontemperature was then raised to 70° C. The ally alcohol was addeddropwise to the reactor over a period of 30 min, while the reactionmixture was maintained at an internal temperature less than 75° C. Asteady reaction exotherm was observed during the addition. The reactionwas stirred at 70° C. for 10 minutes after the addition was complete.FT-IR analysis indicated complete consumption of the allyl double bondsby the disappearance of the C═C stretching bands between 1645 cm⁻¹ and1606 cm⁻¹. The reaction was allowed to cool to below 40° C., at whichpoint excess TMDS was removed by distillation under vacuum. The TMDS waspure, as determined by GC, ¹H NMR and ²⁹Si analysis, and could berecycled. A light yellow oil was obtained as an intermediate.

A 500 mL one-necked round bottom flask was equipped with a refluxcondenser and magnetic stirrer, and placed under gentle nitrogen flow. Asolution of the above intermediate, and 4-vinyl cyclohexene 1,2-epoxide(42 g, 0.34 mol) in toluene (anhydrous, 200 mL) was charged and stirredat 75-85° C. Platinum-cyclovinylmethylsiloxane complex in cyclicmethylvinylsiloxanes (15 mg) was added and the reaction mixture wascontinuously stirred for about 24 h. The reaction process was monitoredby FTIR until the disappearance of the SiH peak (˜2119 cm⁻¹).

The reaction mixture was cooled to 60° C. and3-isopropenyl-α,α-dimethylbenzyl isocyanate (m-TMI, 69 g, 0.34 mol) anddibutyltin dilaurate (0.06 g, 0.1 mmol) were added subsequently. Thereaction process was monitored by FTIR and completed when the isocyanatepeak (˜2260 cm⁻¹) disappeared. The solvent was then removed under vacuumat room temperature and the product was collected as a light yellowliquid with a quantitative yield. The identity of this compound wasconfirmed by ¹H NMR to have the following structure (1F):

Example 2

A solution of 3-cyclohexene-1-carboxaldehyde (30 g, 0.27 mol),2-aminoethyl methacrylate hydrochloride (67 g, 0.4 mol),2-hydroperoxy-2-methylpropane (40 mL, 0.3 mol), CuI (0.5 g, 2.7 mmol),AgIO₃ (0.76 g, 2.7 mmol) and CaCO₃ (60 g, 0.6 mol) in acetonitrile (100mL) was stirred at 40° C. for 24 hr. The reaction mixture was cooled toroom temperature. Oxone (330 g, 0.53 mol) and deionized water (100 mL)were added and the mixture was stirred for 3 hr at room temperature. Thereaction mixture was extracted with toluene and washed with de-ionizedwater. The solvent was then removed under vacuum at room temperature andthe product was collected as a liquid with a quantitative yield. Theidentity of this compound was confirmed by ¹H NMR to have the followingstructure (1H, where R=Me)

Example 3

A solution of 1-methanol-3,4-cyclohexene (9.6 g, 86 mmol), methylmethacrylate (7.5 g, 87 mmol), and methanesulfonic acid (0.5 g, 5.2mmol) in toluene (150 mL) was stirred at 120° C. for 2 hr. The reactionmixture was cooled to room temperature. Sodium bicarbonate (60 g, 0.71mol), axone (120 g, 195 mmol), acetone (100 mL), and deionized water(100 mL) were added and the mixture was stirred for 3 hr at roomtemperature. The reaction mixture was allowed to stand for 1 hr to phaseseparate. The water layer was removed. The organic layer was dried withanhydrous magnesium sulfate and toluene was then removed under vacuum atroom temperature. The final product was collected as a light yellowliquid with a quantitative yield. The identity of this compound wasconfirmed by ¹H NMR and GC-MS to have the following structure,1-methacrylomethyl-3,4-cyclohexene epoxide (1J).

The acrylate version of this monomer can be prepared by the sameprocedure.

Example 4

The polymer compositions in Table 1 were prepared following the sameprocedure which is described here in detail for Polymer I.

TABLE 1 Copolymer compositions (constituent monomers in wt. %) Polymer III III IV V VI VII VIII IX X XI 2-EHA 49.9 50.2 49.6 49.9 49.9 49.9 49.952.1 51.9 51.2 52.0 MA 48.1 48.3 47.8 48.0 48.0 48.0 48.0 46.5 46.4 45.746.2 GMA 1.5 0 2.0 1.5 1.5 1.5 1.5 — 1.5 — — M100 0.5 0.5 — — — — — — —— — OXE-10 — — — 0.6 — — — — — — — 5A — 1.0 — — — — — — — — — 1A — — 0.6— — — — — — — — 1F — — — — 0.6 — — — — — — 1H — — — — — 0.6 — — — — — 3A— — — — — — 0.6 — — — 1J — — — — — — — 1.4 0.2 1.2 0.5 HPMA — — — — — —— — — 2.0 0 HBAGE — — — — — — — — — — 1.3

A four-neck 1 L round-bottom polymerization flask was equipped with athermometer connected to a temperature control device, a condenser, anoverhead mechanical stirrer, two addition funnels, and nitrogeninlet/outlet. The set-up was purged with nitrogen gas for 15 min. Amixture of the following monomers was prepared: 2-ethylhexyacrylate(2-EHA, 99.8 g), methyl acrylate (MA, 96.2 g), glycidyl methacrylate(GMA, 3.0 g), 1-acrylomethyl-3,4-cyclohexene epoxide (M100, 1.0 g). Toone of the funnels was charged 160 g of the monomer mixture. To anotherfunnel was charged the initiator 2,2′-azobis-(2-methyl propionitrile)(AIBN, 0.5 g) and ethyl acetate (60 mL). To the polymerization flask wascharged the remaining monomer mix (40 g), initiator AIBN (0.27 g), andethyl acetate (100 mL). The mixture was heated to vigorous reflux(76-80° C.) and held for 15 minutes. Then, the monomer mix in the funnelwas added continuously over 2 hr at a constant rate. Simultaneously, theinitiator solution in the funnel was added continuously over 3 hr at aconstant rate. Upon complete addition of initiator solution, the mixturewas stirred for an additional 2 hr at reflux. A short half-lifeinitiator (0.75 g) and ethyl acetate (25 mL) were charged into theinitiator funnel and then added into the polymerization flask over 1 hrto reduce residual monomers. The polymerization solution was cooled to60° C. and cationic photoinitiator Cyracure UVI-6976 (1.0 g, 50% inpropylene carbonate) was added and mixed thoroughly for 15 minutes.After ethyl acetate was removed by under vacuum at 55-60° C., acrylicpolymer (I) was obtained with M_(w) of approximately 97,000 determinedby GPC. The viscosity (Brookfield) of the polymer was about 40,000 mPa·sat 135° C. The properties of the adhesive film were as follows: shearresistance (2 kg weight, 25 mm×25 mm area)>168 hr at 21° C. on stainlesssteel panel, peel strength 19 N/25 mm on stainless steel panel, looptack 23 N/25 mm on stainless steel panel, SAFT 171° C. on PET film and160° C. on an aluminum foil backing.

Example 5

The viscosities at 135° C. of polymers prepared in Example 4 and theircured adhesive film (2 mil, 50 μm) properties on stainless steel weremeasured. Shear resistance was measured using a lkg or 2 kg weight, asindicated, with 25×25 mm bond area. SAFT was measured using both PET andaluminum foil backing films.

TABLE 2 Adhesive properties Viscosity Peel Loop Tack Shear SAFT ° C.Polymer mPa · s N/25 mm N/25 mm hours PET Al I 40,000 19 23 >168 171 160(1 kg) II 52,000 24 28   6 110 125 (2 kg) III 46,000 1924 >168 >190 >190 (1 kg)

Example 6 Comparative Polymer Compositions

Polymers XII and XIII were prepared in the same manner as Example 4.Besides the cationic photoninitators, Cyacure UVI-6976, Polymers XII andXIII were synthesized using a mono-substituted oxirane monomer, andtheir compositions are shown in Table 3.

TABLE 3 Comparative copolymer compositions (constituent monomers in wt.%) Polymer XII XIII 2-EHA 49.9 49.9 MA 48.1 48.1 GMA 2 0 4-HBAGE 0 2

The viscosity at 135° C. of Polymer XII was 46,500 mPa·s initially, andit increased very quickly and gelled in less than 2 hr.

The viscosity at 135° C. of Polymer XIII was 38,750 mPa·s initially, andit increased 10% at 135° C. in 7 hours. The adhesive film was not fullycured upon UV irradiation and had no green strength. However, itcontinued the dark-cure in 24 hours. The shear strength of the adhesivefilm, after one week of dark-cure, was >168 hr (2 kg, 25 mm×25 mm) at21° C. on stainless steel panel.

Example 7

An adhesive formulation was made using the acrylic polymer (VIII) ofExample 4 (75 wt %), Kristalex® F85, Eastman, Netherland (15 wt %), andEVA 28-150 (10 wt. %). Peel adhesion values, measured at 20 minutes and24 hours with stainless steel 50 μm PET, are listed in Table 4.

TABLE 4 Peel adhesion from stainless steel 50 μm PET Dose (mJ/cm²) UVC20 g/m² 40 g/m² 60 g/m² 100 g/m² Peel Adhesion (N/25 mm) at 20 minutes 515.2 16.8 21.0 21.3 10 12.8 16.2 18.8 22.5 20 3.6 15.9 16.1 22.2 40 12.517.0 18.5 19.1 60 12.5 15.7 17.4 20.0 Peel Adhesion (N/25 mm) at 24hours 5 23.1 23.1 32.5 29.9 10 18.0 25.1 28.3 38.9 20 12.2 23.5 23.537.4 40 15.3 17.1 25.4 30.9 60 16.2 21.3 24.2 30.5 All peel adhesionresulted in adhesive failure mode

The peel adhesion values indicate that the cationic formulation can becured at a variety of dose levels and coat weights typically used in thetapes and labels industry.

SAFT experiments were conducted from 40 to 200° C. at 1 kg load, bondarea 25 by 25 mm, on mirrored stainless steel, and the failuretemperatures are shown in Table 5. Hot shear resistance results are alsoshown in Table 5.

TABLE 5 SAFT test and Shear test results Dose (mJ/cm²) UVC 20 g/m² 40g/m² 60 g/m² 100 g/m² SAFT (° C.) 5 >200* >200* >200* 127° C.10 >200* >200  >200* 170° C. 20 >200* >200* >200* >200* 40 178° C. 178°C. >200* >200* 60 177° C. >200* >200* >200* Hot Shear Resistance (hrs)5 >120* >120* >120* >120* 10 >120* >120* >120* >120*20 >120* >120* >120* >120* 40 >120* >120* >120* >120*60 >120* >120* >120* >120* *Test was terminated before failure occurred.

The results from the SAFT experiment in Table 5 indicate that theadhesive can maintain high temperature holding. The results from the hotshear resistance experiment in Table 5 demonstrate that the adhesive hasa robust curing window because it cures completely over a wide range ofUVC doses and coating weights.

Example 8

A first set of adhesive films having compositions according to theexamples listed in Table 6 were coated at 25° C., 50% RH, on releaseliner, dried, UV cured and then laminated to PET film backing in theusual manner in preparation for peel adhesion testing.

A second set of adhesive films, following coating and drying were placedin a chamber set to a controlled environment of 25° C., 50% RH, for 72hours, with one adhesive surface exposed to the air. After conditioningfor 72 hours, the films were then UV cured and laminated. Adhesiveproperties for the two sets of adhesive films are compared in Table 6.

TABLE 6 Cured adhesive properties following exposure to moisture Coatedat 25% RH and 25° C. and UV cured Exposed to Coat Dose immediately 50%RH and 25° C. Weight (mJ/cm²) following for 72 hours (g/m²) UVC coatingbefore UV curing Peel N/25 mm N/25 mm Ex 11 67 60  27.1  25.0 Ex 9 60 80 28.1  20.0 Polymer X 60 80  16.9  12.7 SAFT ° C. ° C. Ex 11 67 60167-200 >200* EX 9 60 80 >200* >200* Polymer X 60 80 >200* >200* HotShear Hrs Hrs Ex 11 67 60 127-168 >168* EX 9 60 80 >168* >168* Polymer X60 80 >168* >168* *Test was terminated before failure occurred.

The presence of water in cationic epoxies during UV curing usuallyquenches the propagating superacid species, leading to decreasedcrosslinking, and thereby decreases cohesive properties in the adhesive.Surprisingly, the above results indicate that the presence of waterresulting from exposure to a humid environment did not negatively affectthe cured adhesives of this invention.

Example 9

A formulation was made of Polymer VIII (90 wt %) and Foral 85E (10 wt%), and the adhesive properties are summarized in Table 7.

TABLE 7 Adhesive properties with the addition of a tackifier Coat UVCDose Weight (mJ/cm²) (g/m²) 20 min Peel (N/25 mm) 24 hrs (N/25 mm) 60 60 11.9 12.4 125 60  10.7 13.1 Failure temp SAFT (° C.) 60 60 >200* 12560 >200* Hot shear Hrs 60 60 Not tested 125 60 >168* *Test wasterminated before failure occurred.

Surprisingly, the above results indicate that addition of tackifier didnot negatively affect the adhesive properties.

Example 10

A formulation was made of Polymer VIII (80 wt %), Foral 85E (10 wt %)and Licocene® PP 1302, Clariant (10 wt %) and the adhesive propertiesare summarized in Table 8.

TABLE 8 Adhesive properties with the addition of a tackifier and anethylene copolymer Dose Coat Weight (mJ/cm²) UVC (g/m²) 20 min 24 hrsPeel (N/25 mm) (N/25 mm) 60 80  18.9 20.4 Failure temp SAFT (° C.) 6080 >200* Hot shear Hr 60 80 Not tested 60 20 >168* *Test was terminatedbefore failure occurred.

Surprisingly, the above data indicates that the addition of thepolyethylene copolymer improves the peel adhesion of the adhesivewithout the loss of cohesion in comparison to Example 9 under similarconditions of coat weight and UV dose.

Example 11

An adhesive formulation was made using the acrylic Polymer VIII (80 wt%), Kristalex F85 (20 wt %), and the adhesive properties are summarizedin Table 9.

TABLE 9 Adhesive properties with the addition of an aromatic tackifierDose (mJ/cm²) Coat Weight UVC (g/m²) Peel 20 min 24 hrs 60 63  17.0 25.0115 115  20.0 26.9 Failure temp SAFT (° C.) 60 63 >200* 115 115 >200*Hot shear Hours 60 63 >168* 115 115 >168* *Test was terminated beforefailure occurred.

Typically, the addition of tackifier in adhesive results in lowercohesive properties. An aromatic tackifier is expected to result in evengreater loss of cohesion due to strong UV absorption by the aromaticrings. Surprisingly, the above data indicates that even an addition of20% aromatic tackifier in the formulation resulted in good adhesiveproperties.

FIG. 1 shows the viscosity over time for Polymer VIII and Polymer IX.The viscosity of each sample was measured by a Brookfield viscometer at130° C. Polymer VIII, according to this FIG. 1, had a stable viscosityaround 45,000 mPa·s for about 300 minutes. The formulated adhesive,Examples 9, also exhibited stable viscosity, even up to 140° C., whichindicates a long usable pot life.

Many modifications and variations of this invention can be made withoutdeparting from its spirit and scope, as will be apparent to thoseskilled in the art. The specific embodiments described herein areoffered by way of example only, and the invention is to be limited onlyby the terms of the appended claims, along with the full scope ofequivalents to which such claims are entitled.

The invention claimed is:
 1. An ultra-violet curable pressure sensitiveadhesive comprising an acrylic polymer and a cationic photoinitiator,wherein said acrylic polymer is prepared from the group consisting of:(i) an acrylic monomer consisting of an acrylic or methacrylic acidderivative of the formula CH₂═CH(R₁)(COOR₂), wherein R₁ is H or CH₃ andR₂ is C₁₋₂₀ alkyl chain; (ii) a monomer, wherein said monomer comprisesa pendant reactive functional group selected from cycloaliphaticepoxide, oxetane or mixtures thereof, and contains from about 0.001 toabout 0.015 equivalent per 100 g of said acrylic polymer; wherein theacrylic polymer (a) is essentially free of multi-(meth)acrylate, (b) hasa Tg value less than 0° C., and (c) has a weight average molecularweight from about 50,000 to about 1,000,000 g/mol; and wherein theultra-violet curable pressure sensitive adhesive has a viscosity rangeof 1,000-500,000 mPa·s at 80-180° C.
 2. The ultra-violet curablepressure sensitive adhesive of claim 1 wherein the (ii) monomer containfrom about 0.002 to about 0.010 equivalent per 100 g of the acrylicpolymer.
 3. The ultra-violet curable pressure sensitive adhesive ofclaim 1 wherein the (ii) monomer is a cycloaliphatic epoxide having theformula:

wherein R¹ is O, S, C═O, or linear, branched, or cyclic alkylene, oroxyalkylene, arylene, R² is linear, branched, and cyclic alkyl oralkoxy, aryl, H, halogen, C═O, or part of R¹ as fused cycloaliphaticring through a covalent bond connection, R³ is (CH₂)_(n), n=0-3, X isacrylate or methacrylate, or comprises a —W—Y group, where W is O, S,amide, carbonate, urethane, urea, siloxane or a combination thereof, andY is —R⁴—C(R⁵)═CH₂, where R⁴ is a linear or branched C₂₋₁₀ alkylene,C₂₋₁₀ oxyalkylene, C═O, or arylene or derivative thereof, and R⁵ is H orCH₃.
 4. The ultra-violet curable pressure sensitive adhesive of claim 1wherein the cycloaliphatic epoxide has the formula:

where R¹═H or CH₃, or mixtures thereof.
 5. The ultra-violet curablepressure sensitive adhesive of claim 4 wherein the cycloaliphaticepoxide is:

or mixtures thereof.
 6. An ultra-violet curable pressure sensitiveadhesive comprising an acrylic polymer and a cationic photoinitiator,wherein said acrylic polymer is prepared from: (i) an acrylic monomerconsisting of an acrylic or methacrylic acid derivative of the formulaCH₂═CH(R₁)(COOR₂), wherein R₁ is H or CH₃ and R₂ is C₁₋₂₀ alkyl chain;(ii) a monomer, wherein said monomer comprises a pendant reactivefunctional group that is present from about 0.001 to about 0.015equivalent per 100 g of said acrylic polymer; wherein the acrylicpolymer (a) is essentially free of multi-(meth)acrylate, (b) has a Tgvalue less than 0° C., and (c) has a weight average molecular weightfrom about 50,000 to about 1,000,000 g/mol; and wherein the pendantreactive functional group is a benzophenone having the formula:

where Z is S, O, CH₂, or NH, R¹⁻⁸ are independently H, Cl, Br, I, F,C₁₋₂₄ alkoxy, C₁₋₂₄ alkyl, or aryl; and wherein at least one of R¹⁻⁸must comprise a —W—X—Y group, where W is a C₁₋₁₂ alkylene or C₁₋₁₂oxyalkylene, X is carbonate, urethane, urea, tetramethyldisiloxane or acombination thereof, and Y is —R⁹—C(R¹⁰)═CH₂, where R⁹ is a linear orbranched C₂₋₁₀ alkylene or C₂₋₁₀oxyalkylene, or arylene or derivativethereof, and R¹⁰ is H or CH₃.
 7. The ultra-violet curable pressuresensitive adhesive of claim 6 wherein the benzophenone has the formula:

or mixtures thereof.
 8. The ultra-violet curable pressure sensitiveadhesive of claim 1, wherein the cationic photoinitiator has thestructure of

where R is C₃H₇, C₁₂H₂₅, W is S, SO, SO₂ or CO.
 9. The adhesive of claim8 wherein the cationic photoinitiator is:

where R¹ and R² are independently H, CH₃, C₂H₅, C₃H₇, C₁₂H₂₅, OCH₃,OC₂H₅, OC₃H₇, or OC₁₂H₂₅.
 10. The ultra-violet curable pressuresensitive adhesive of claim 1 further comprising a polyethylenecopolymer additive.
 11. The ultra-violet curable pressure sensitiveadhesive of claim 10, wherein the adhesive has a solvent content of lessthan about 2% by weight of the total adhesive.
 12. An article ofmanufacture comprising the adhesive of claim
 11. 13. An ultra-violetcurable pressure sensitive adhesive comprising an acrylic polymer and acationic photoinitiator, wherein said acrylic polymer comprises: (i) anacrylic monomer consisting of an acrylic or methacrylic acid derivativeof the formula CH₂═CH(R₁)(COOR₂), wherein R₁ is H or CH₃ and R₂ is C₁₋₂₀alkyl chain; (ii) a monomer, wherein the monomer comprises a pluralityof pendant reactive functional groups selected from (1) mono-substitutedoxirane, and (2) cycloaliphatic epoxide, oxetane, benzophenone ormixtures thereof, and wherein said monomer contains from about 0.001 toabout 0.015 equivalent per 100 g of said acrylic polymer; wherein saidacrylic polymer (a) is essentially free of multi-(meth)acrylate (b) hasa Tg value less than 0° C., and (c) has a weight average molecularweight from about 50,000 to about 1,000,000 g/mol; and wherein thependant reactive functional group comprises a benzophenone having theformula:

where Z is S, O, CH₂, or NH, R¹⁻⁸ are independently H, Cl, Br, I, F,C₁₋₂₄ alkoxy, C₁₋₂₄ alkyl, or aryl; and wherein at least one of R¹⁻⁸must comprise a —W—X—Y group, where W is a C₁₋₁₂ alkylene or C₁₋₁₂oxyalkylene, X is carbonate, urethane, urea, tetramethyldisiloxane or acombination thereof, and Y is —R⁹—C(R¹⁰)═CH₂, where R⁹ is a linear orbranched C₂₋₁₀ alkylene or C₂₋₁₀oxyalkylene, or arylene or derivativethereof, and R¹⁰ is H or CH₃.
 14. The ultra-violet curable pressuresensitive adhesive of claim 13 wherein the benzophenone has the formula:

or mixtures thereof.
 15. The ultra-violet curable pressure sensitiveadhesive of claim 13, wherein the pendant reactive functional groupcomprises a mono-substituted oxirane having the formula:

where R¹═H or CH₃ or mixtures thereof.
 16. The ultra-violet curablepressure sensitive adhesive of claim 13, wherein the cationicphotoinitiator has the structure of

where R is C₃H₇, C₁₂H₂₅, W is S, SO, SO₂ or CO.
 17. The adhesive ofclaim 16 wherein the cationic photoinitiator is:

where R¹ and R² are independently H, CH₃, C₂H₅, C₃H₇, C₁₂H₂₅, OCH₃,OC₂H₅, OC₃H₇, or OC₁₂H₂₅.
 18. The ultra-violet curable pressuresensitive adhesive of claim 13 further comprising a polyethylenecopolymer additive.
 19. The ultra-violet curable pressure sensitiveadhesive of claim 18, wherein the adhesive has a solvent content of lessthan about 2% by weight of the total adhesive.
 20. An article ofmanufacture comprising the adhesive of claim
 13. 21. The adhesive ofclaim 6, wherein the cationic photoinitiator has the structure of

where R is C₃H₇, C₁₂H₂₅, W is S, SO, SO₂ or CO.
 22. The adhesive ofclaim 21 wherein the cationic photoinitiator is:

where R¹ and R² are independently H, CH₃, C₂H₅, C₃H₇, C₁₂H₂₅, OCH₃,OC₂H₅, OC₃H₇, or OC₁₂H₂₅.
 23. The ultra-violet curable pressuresensitive adhesive of claim 6 further comprising a polyethylenecopolymer additive.